1. Field of the Invention
The invention relates to a vehicular brake force control apparatus and a vehicular brake force control method, and more particularly, a vehicular brake force control apparatus and a vehicular brake force control method that control a brake force when engine brake is acting.
2. Description of the Related Art
As one type of brake force control apparatus for vehicles such as an automobile, a brake force control apparatus has been known that controls a brake force of each wheel while taking into consideration engine brake. For example, Japanese Patent Laid-Open Publication No. JP-A-10-264791 discloses a brake force control apparatus in which a target brake force is calculated based on a depression amount of a brake pedal; a brake force for driven wheels is derived from negative torque of a drive power source; and a brake force distribution ratio for the brake forces that it is necessary to distribute to the driven wheels and non-driven wheels is determined based on the driving conditions of the vehicle. Then, a brake command value for the driven wheels and the non-driven wheels is derived based on the target brake force, the brake force distribution ratio, and the negative torque portion (engine brake force) of the drive power source, and finally, the brake force of each wheel is controlled based on the command value.
Moreover, Japanese Patent Laid-Open Publication No. JP-A-10-264791 discloses a brake force control apparatus for a rear-wheel drive vehicle that, when engine brake is acting on the rear driven wheels, increases a brake force of the front wheels such that a brake force distribution of the front and rear wheels becomes appropriate.
However, with the conventional brake force control apparatus like that disclosed in Japanese Patent Laid-Open Publication No. JP-A-10-264791, the brake forces of the driven wheels and the non-driven wheels are controlled based upon the target brake force, the brake force distribution ratio, and the engine brake force. When engine brake is acting, the brake force of the non-driven wheel is always controlled by operation of a friction brake device. Accordingly, load of the friction brake device of the non-driven wheel increases, and durability of the friction brake device is liable to be reduced.